1. Field of the Invention
The present invention relates to methods and apparatus for fabricating integrated circuits and more particularly to such circuits upon which conductive bumps are formed for providing a contact point to which a lead can be bonded.
2. Description of the Related Art
One means for connecting conductive leads to an integrated circuit die is known as tape-automated bonding (TAB). In the TAB process, an elongate continuous film includes a plurality of lead frames formed sequentially thereon. During the manufacturing process, an integrated circuit die is mounted on the inner ends of the leads in a frame. The outer ends of the leads may then be used to connect the integrated circuit with other components.
When processing a wafer which includes ICs that are to be used in the TAB process, special steps are taken to create conductive bumps to which the inner leads of the TAB frame can be heat bonded. Completed wafers are first sputter etched and then deposited with a barrier metal film of titanium/tungsten. The titanium/tungsten layer provides a suitable surface for a thin (approximately 1 or 2 microns) layer of gold which is plated thereover. Photoresist is spun onto the wafer in a layer 30 microns thick and exposed and developed to leave an opening over each die bond pad. The exposed portions of the wafer are then electroplated with gold by using an electrode to contact the thin film layer. Thereafter the photoresist is stripped and the gold and titanium/tungsten thin films are etched away leaving the wafer with 1 mil high gold bumps over each bond pad.
Each bump provides a mechanical stand-off from the surface of the IC thus preventing lead shorting to the IC and/or physical damage to the IC during the process of bonding the inner leads on the TAB frame to the gold bumps.